# server.open

- **Type:**

```ts
type Open =
  | boolean
  | string
  | string[]
  | {
      target?: string | string[];
      before?: () => Promise<void> | void;
    };
```

- **Default:** `undefined`

`server.open` is used to configure a set of page URLs that Rsbuild will automatically open in the browser after starting the server.

> You can also use the [--open](/guide/basic/cli#opening-page) option of Rsbuild CLI to open the pages. When using `server.open` and `--open` at the same time, `--open` takes precedence.

## Example

`server.open` can be set to the following values.

- Open the project's default preview page, which defaults to `http://localhost:<port>`. If [server.host](/config/server/host) is configured, it defaults to `http://<host>:<port>`.

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: true,
  },
};
```

- Open the specified page:

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: 'http://localhost:3000',
  },
};
```

- Open the specified path, equivalent to `http://localhost:<port>/home`:

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: '/home',
  },
};
```

- Open multiple pages:

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: ['/', '/about'],
  },
};
```

- Open a non-localhost URL (used with proxy):

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: 'http://www.example.com',
  },
};
```

## Port placeholder

The port number that Rsbuild server listens on may change. For example, if the port is in use, Rsbuild will automatically increment the port number until it finds an available port.

To avoid `server.open` becoming invalid due to port changes, you can use one of the following methods:

- Enable [server.strictPort](/config/server/strict-port).
- Use the `<port>` placeholder to refer to the current port number. Rsbuild will replace the placeholder with the actual port number it is listening on.

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: 'http://localhost:<port>/home',
  },
};
```

## Specify browser

Rsbuild opens pages in the system default browser by default, and also supports specifying which browser to use when starting the dev server through the `BROWSER` environment variable.

### Browser name

Rsbuild uses the [open](https://github.com/sindresorhus/open) library to open browsers, and supports opening Chrome, Edge, and Firefox:

```bash
# Chrome
BROWSER=chrome npx rsbuild dev

# Edge
BROWSER=edge npx rsbuild dev

# Firefox
BROWSER=firefox npx rsbuild dev
```

On Windows, use [cross-env](https://npmjs.com/package/cross-env) to set environment variables:

```bash
npm i cross-env -D
cross-env BROWSER=chrome npx rsbuild dev
```

You can also refer to the [app option](https://github.com/sindresorhus/open?tab=readme-ov-file#app) of `open` to configure more special `BROWSER` values, such as some OS-specific browser names:

```bash
# macOS
BROWSER="google chrome" npx rsbuild dev

# Linux
BROWSER="google-chrome" npx rsbuild dev
```

### Browser arguments

Pass browser arguments through `BROWSER_ARGS`, with multiple arguments separated by spaces:

```bash
BROWSER=chrome BROWSER_ARGS="--incognito" npx rsbuild dev
```

### AppleScript

On macOS, Rsbuild also supports opening the browser through AppleScript, which allows you to reuse existing browser tabs to open pages.

The following are the browser names supported by AppleScript:

- Google Chrome Canary
- Google Chrome Dev
- Google Chrome Beta
- Google Chrome
- Microsoft Edge
- Brave Browser
- Vivaldi
- Chromium

For example:

```bash
BROWSER="Google Chrome Canary" npx rsbuild dev
```

### Configure env variable

You can set the `BROWSER` environment variable in the local [.env.local](/guide/advanced/env-vars#env-file) file, so you don't need to manually set the environment variable every time you start the dev server, and it also avoids affecting other developers in the project.

```bash
# .env.local
BROWSER=chrome
```

## Callback

By using `open.before`, you can trigger a callback function before opening the page.

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: {
      before: async () => {
        await doSomeThing();
      },
    },
  },
};
```

When using `open.before`, the page URLs can be configured via `open.target`.

```ts title="rsbuild.config.ts"
export default {
  server: {
    open: {
      target: ['/', '/about'],
      before: async () => {
        await doSomeThing();
      },
    },
  },
};
```
